The present invention relates to a direct current motor and more particularly to a direct current motor which is improved with respect to commutating characteristics, by use of short-circuit means capable of short-circuiting a predetermined number of armature coils which constitute a wave winding type armature, whereby the armature is reduced in thickness and formed in a disc- or cylindrical shape.
It is well known that a direct current (DC) motor, provided with a plurality of armature coils formed in a lap winding manner or a wave winding manner is highly efficient and has better commutating characteristics as the number of armature coils increases. However if the conventional manner of lap winding or wave winding is employed in a coreless motor, the armature will increase in thickness because the armature coils are superimposed on each other in many layers. The increased thickness of the armature will substantially reduce the effective magnetic field of the field magnet which passes through the armature, resulting in decreased magnetic field, motor efficiency and starting torque. In order to solve these problems, the prior art effort has been directed to decreasing the thickness of the conductor portions contributing to the generation of torque. This process for decreasing the thickness of the conductor portions is performed by press molding, and accordingly is often accompanied by such defects as breaking and short-circuiting of the armature coils. Further, since the phase relationship between the armature coils cannot be positively held in the desired state at the time the coils are arranged, correct phase relationship between the windings is liable to be distorted. Accordingly, such prior art DC motors are costly and cannot be mass produced.
Another prior art technique used for conventional cylindrical coreless DC motors, for avoiding superimposition of the opposite edge portions of the armature coils on each other, requires that the insulated wire be wound in alignment, turn by turn, alternatingly at an angle of about 180.degree., so that a cylindrical armature is formed, with the entire width of winding, or a part thereof slanting with respect to the rotating axis. This technique, however, also is costly and cannot be used for mass-production.